Sounds like to need to...how do I saw this...re-enforce or re-solidify the dream body. You need to turn your attention away from your real body and project your identity onto a fixed symbol in the dream.

One way of doing this is to...move. Run or jump around. But since that is giving you trouble, focus strongly and single pointedly on your hands. Rub them together and focus on the heat friction generates. Continue to stabilize and do some reality checks. Do something you can't do in real life to define a new set of laws in the dream state. Maybe try moving by flying or simply hovering.

Hmm...is that good? Does that make sense?